The present invention relates to current limiting circuits and more particularly to current limiting circuits for DVD disk drives.
In a disk, such as DVD or DVD-RAM, information is recorded in sector units. Each sector includes header information having a physical identification data (PID) area and a user data area. The header information may be recorded on the first sector of the track. Typically, the header information area is divided into peak header area and a bottom header area, and the user data area being divided into a land area and a groove area.
In DVD-RAM disks, a track is formed spirally, and the track is shifted laterally at a predetermined reference point. The reference point usually becomes a starting point of the first sector.
Additionally, as it is known in the art, there exists a need in computer and other types of systems to provide fault-tolerant and redundant circuits. In such systems, when the circuit board or circuit component fails and thus requires replacement, it is often desirable to replace the circuit board or circuit component without removing the operating power from the system. Thus, in these cases, it is necessary to remove the faulty board or circuit component from the system while the system is still operating, and in a simpler matter, it is necessary to install a repaired or new circuit board or circuit component into the system which already has power being provided thereto. That is, the replacement circuit board or circuit component is inserted into a so-called xe2x80x9clivexe2x80x9d or xe2x80x9chotxe2x80x9d system. Similarly, in DVD systems, the same problem occurs during the removal of the medium, from fingerprints and scratches, etc. on the DVD disk. This results in a large noise being introduced in the peak detector in the form of current or voltage. These large current or voltage spikes which results from the removal or the installation of a circuit board or circuit component or from the peak detector detecting signals on the DVD disk from the fingerprints and scratches, causing the system voltage to drop to unacceptable levels. The drop in supply voltage is due to the inability of the power supply to source the necessary current. As electrical charge collects, due to the capacitive effects, the current will decrease until a steady state current is reached in the power supply returns to the nominal level. However, such an operation requires a large amount of time to return back to these nominal levels.
FIG. 1 illustrates one such circuit where the input voltage is input to the gate of a transistor 100. If this input voltage rises rapidly, a large current will flow from the collector to the base of the transistor 100. This additional current will flow through resistor 102 and charge up capacitor 106 increasing the peak hold voltage which is output from the circuit.
FIG. 2 illustrates the increasing voltage and corresponding change in current as illustrated by curve 202. It is required to have a circuit that will respond when subjected to large currents to return quickly to nominal values.
The present invention provides a circuit that will provide a constant current with a large noise current. The current is limited by the operation of a FET.